Carbon nanotubes have been studied for use in various technical fields because of their unique properties not found in other materials such as graphite and diamond in the related art. For example, carbon nanotubes are studied for use in electrodes of electric storage devices. For example, a carbon nanotube composite in which carbon nanotubes are formed in a laminate can be used as an electrode (especially negative electrode) of an electric storage device such as a lithium ion capacitor.
One of carbon nanotube composites known in the related art is a carbon nanotube composite in which a carbon nanotube array is formed on a “multilayer substrate (laminate) having a structure in which a bonding layer, an interface layer, and a catalyst layer are laminated on an inert support” (refer to Reference 1).
According to the description of JP 2015-530961T (Reference 1), the carbon nanotube composite is manufactured as follows. That is, after a multilayer substrate (laminate in which an iron bonding layer, an aluminum interface layer, and an iron catalyst layer are respectively formed on both sides of an aluminum foil) is annealed at 550° C. under an inert gas flow, carbon source gas is introduced at 550° C. Thereafter, the multilayer substrate is heated to a growth temperature of 630° C., and held at the growth temperature for 5 minutes to grow carbon nanotubes on the multilayer substrate. As described above, the carbon nanotube composite is manufactured.
The multilayer substrate used in the method of manufacturing the carbon nanotube composite described in Reference 1 improves bonding of the aluminum interface layer to the inert support body (aluminum foil) by providing the iron bonding layer.
On the other hand, the inventors of the present application have studied formation of carbon nanotubes in a laminate (laminate not having the iron bonding layer as in Reference 1) in which a catalyst layer including a buffer layer and seed catalyst particles is formed on a conductive base material. Furthermore, in this case, as a result of studying to reduce an introduction temperature of carbon source gas for prevention of aggregation of the seed catalyst particles, the followings have been found.
If the introduction temperature of the carbon source gas is reduced, the growth of the carbon nanotubes occurs when the bonding between the buffer layer and the conductive base material is poor. Therefore, it has been found that the buffer layer peels off from the conductive base material due to interface stress generated at an interface between the buffer layer and the conductive base material when the carbon nanotubes grow. Specifically, it has been found that the buffer layer peels off from the conductive base material due to an increase in interface stress caused by a difference in thermal expansion between the buffer layer and the conductive base material and an increase in interface stress caused by pulling of the buffer layer in a growth direction of the carbon nanotubes as the carbon nanotubes grow. This case is not desirable because, in the carbon nanotube composite, a region is formed in which a surface of the conductive base material is exposed with no carbon nanotubes formed thereon.
Thus, a need exists for a method of manufacturing a carbon nanotube composite and a laminate for use in the manufacturing method, which are not susceptible to the drawback mentioned above.